This falls under the phrase "everything affects everything" On the dyno you
may find that a particular combination of cams and exhaust headers has one or
more dips in the HP curve. So, it is not possible to hold a steady load on the
way up. So the engine gets to lump (A) and will not pull higher, so you back off
the load just a bit and let the engine through the trouble RPM and then pile on
the load again until you get to lump (B). Then repeat. This is of no matter, so
long as the problem RPM are not where you use the engine. Typical RPM for us
with only stock rods being legal, was 6,800 to 8,000 RPM. So the driver had to
be in a gear that would give him above 6,800 on the start as lump (B) was at
5800 RPM. Many cars have such problems and they do not show up until the aero
load is high enough to make a dip in HP obvious at a particular RPM. A carb
getting standoff and going over rich, or shaking so hard it foams the fuel
and goes over rich then over lean right after that when the carb calms
down.
Advantage fuel injection.
So it is not only possible it is common if you dyno down low in the RPM
range. It is less common in higher RPM ranges, and is more likely a result of a
more subtle cause. Exhaust back pressure spike. Unhappy distance between intake
horn and flat air cleaner cover. Harmonics in any system changing an output.
Boundary layer separation in front of an intake. A standing wave fooling a
sensor. And about 500 more major possible faults, including your hat is too
tight, or your sectional is improperly folded..
If you can dive a bit from your best speed to a bit higher speed and then
hold the new speed for some time, you may have such a problem.
If you just slow to the original speed then you probably do not. Drag
increases at the cube of velocity, so steps up from best speed require more
effort on clean up, and, or more power.
Lynn E. Hanover
In a message dated 7/9/2012 2:23:24 P.M. Eastern Daylight Time,
rwstracy@gmail.com writes:
The effect you mentioned is true but whether it is significant or not
will depend on the shape of your HP curve which depends in turn on the design
of intake, exhaust, etc. Torque curve is probably pretty flat around
6200 so not too likely to be a big factor.
But more significantly, was that 150 IAS, TAS, or GPS? Were you at
WOT? I've forgotten what the AC type was so don't know how to judge the
results from just this figure.
Tracy